Carbonatitic dykes during Pangaea transtension(Pelagonian Zone, Greece)

Schenker, Filippo and Burg, Jean-Pierre and Kostopoulos, Dimitrios and Baumgartner, Lukas and Bouvier, Anne-Sophie (2018) Carbonatitic dykes during Pangaea transtension(Pelagonian Zone, Greece). UNSPECIFIED. Lithos, 302. pp. 329-340. ISSN 0024-4937

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Carbonatitic dykes surrounded by K-Na-fenites were discovered in the Pelagonian Zone in Greece. Their carbonate portions have an isotopic mantle signature of δ13C and δ18O ranging from -5.18 to -5.56 (‰ vs. VPDB) and from 10.68 to 11.59 (‰ vs. VSMOW) respectively, whereas their mafic silicate portions have high Nb, Ta and ɛNd values, typical of alkaline basalts. Textural relationships hint at a cogenetic intrusion of silicate and carbonate liquids that according to antithetic REE profiles segregated at shallow depths (<0.6 GPa) from a parental melt sourced deeper in the mantle. Fenites bear similar REE abundances to mafic rocks but with high Rb-Ba and low Nb-Ta values. SHRIMP II U-Pb analyses of magmatic zircon cores (δ18O=7.21-7.51) from a carbonate-bearing syenitic amphibolite yielded a Permian intrusion age at 278±2 Ma, considerably older than a Cretaceous (118±4 Ma) greenschist overprint obtained from metamorphic zircon rims (δ18O=6.78-7.02). From 300 to 175 Ma the ɛNd of the Pelagonian magmatism rose irregularly to more primitive values attesting to a higher increment of asthenosphere-derived melts. In this context, the carbonatite formed within a transtensional regime of an intra-Pangaea dextral transform fault that signalled the forthcoming penetrating breakoff of the supercontinent, manifested in the Permo-Triassic.

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